From your post, I can't quite decide what worries you most about this relationship... I've written and rewritten this comment multiple times because of that.

The usual concern with such an age gap would be that he might take advantage of her and her lack of experience. That's a valid concern that should be addressed. But It doesn't seem to be what's bothering you.

With you starting your post by telling us about his ex who is completely irrelevant to this story and your relationship with her, then later list off how great your son is and that "it’s not like he’s lacking options"... I can't shake the feeling that your problem is more with him having a partner that could be considered "below his own status". It feels like you would react just the same if he dated someone closer to his age but not as successful or good-looking. And to that I must say, that's none of your business. Let your son love whoever he wants to love. Let him make his own decisions and when it comes to it, his own mistakes. They obviously share some interests and he's old enough to decide if she's "good enough" for him.